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Old 28th December 2011, 06:41 AM   #11
dgta is offline dgta  United States
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CONCLUSION

I did correspond with the seller. The "calibration manual" does not exist. He just reprinted parts of the regular 752 user's manual. The whole 752 manual copy is available on eBay and elsewhere for $10-15. Apparently with no copyright issues.

There is no evidence that Hickok ever supplied any other "special" or "additional" info to the FAA, government or anyone else. Nor is there any evidence that FAA or other gov't entity ever generated any such documents relating to the 752.

Last edited by dgta; 28th December 2011 at 06:47 AM.
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Old 4th January 2012, 03:21 PM   #12
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Default 752/752A calibration

There is little difference between ANY Hickok tester...more or better bells and whistles it about it. They ALL are built on the same model for measuring, PERIOD. If you can follow the proceedure for a 6000 or a 539 a or b series calibration then you can figure it out on your own. The 752 is very close to the 539/539b in many ways ( bells and whistles to improve the accuracy, which was NEVER meant, on any HICKOK, to be a LAB tester period...including the C).

There is little reason to fiddle with the guts unless you have replaced the 83 and or 5Y3 with a poor balanced-sides tubes. The 752 allows one to adjust the amplitude of mismatched 120hz pulses ( the 539 series also allows the adjustment for the 5Y3) which DOES affect the gm reading by adding to the plate current and for the 5Y3 by adding to the grid signal offset). ( in other words R20 offsets (equalizes) the peaks of the 83, the 5Y3 is not adjustable unless you add a pot). BUT, if you have a well ballanced tube to begin with, the issue is minimum.

If you have 150 plate, 130 screen, 40 bias per 6000 or any Hickok calibration instruction, then leave it alone! Remember Hickok allowed a good 5% allowance on these values plus or minus. If you have a digital meter you MUST add the right amount of resistance across your probe tips or you will read the plate and screen wrong ( your plate might read 190 when it is really 150).

The one series of testers to try to avoid is any that used the 'english dot' to set the meter sensitivity. The dual pot is 9 of 10 times worn out and or grimmy and repairing one is close to brain surgery, not to mention poor on accuracy the day it was made. Done to many, I know what I speak.

and DO NOT USE DeOxit on any wafer or you just bought yourself a boat anchor. In fact, put deoxit in the next room with your stereo and away from test gear. It IS conductive oil and creates tiny leakage circuits a tester will pick up an a bad tube.

Last, everyone thinks tinkering with these will make it digital age accurate. It will not. Every Hickok tester will give slightly different results even from the same make/model and across models is even worse. They were never intended to decide if an eBay seller is ripping you off by claiming his tube reads 100 points higher than you tester says.

This is NOT rocket science. If you have the ability to read and follow, and can handle the maze of wires, you don't need to send it off and wait two years to get it back from California. USE an isolation transformer, that is a must. Study and understand before you begin. Google, BAMA, and a host of others have all the info you need, so go seek it or mail the tester off.

Good luck
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Old 4th January 2012, 04:24 PM   #13
Bill_P is online now Bill_P  United States
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Quote:
Originally Posted by glassandlight View Post

and DO NOT USE DeOxit on any wafer or you just bought yourself a boat anchor. In fact, put deoxit in the next room with your stereo and away from test gear. It IS conductive oil and creates tiny leakage circuits a tester will pick up an a bad tube.
I assume your comment is experience based. The maker of deoxit has a different opinion: WARNING: Alcohol / ethanol are conductive
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Old 4th January 2012, 04:28 PM   #14
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well, you do what YOU think is best. But if you put it on, you can NOT remove it...it is a one way street.
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Old 4th January 2012, 11:56 PM   #15
dgta is offline dgta  United States
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Easy enough to test. Take a clean piece of plastic, make sure it tests as infinite resistance. Spray Deoxit. Let dry. Measure resistance again.
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Old 5th January 2012, 12:04 AM   #16
mksj100 is offline mksj100  United States
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Most Hickok testers operate very similarly and most use the same circuit with some minor modifications. The Daniel Shoo article on calibration of the Hickok 539 in AUdioXpress does not seem to pull up with the links provided, but is accessible by pasting the following URL in your browser to directly pull up the PDF file "http://www.circuitcellar.com/AAI/media/schoo2798.pdf". There is also some additional information at the following posting on ARF Antique Radio Forums • View topic - Updated Hickok 539 Calibration document.

In general there are very few adjustments that can be made in most of these tester, for the 752 the two primary adjustments would be R5 for the line voltage and R20 which adjusts the 83 tube balance. The 539 also allows you to adjust the balance for the 5Y3 tube, so it would be important to have a closely balanced 5Y3 tube in the 752. This was mentioned in the previous post. Make sure the plate/screen voltages are checked with a 1000ohm/v meter as specified in Daniel Shoo's calibration procedure. Also check the signal voltages are correct as noted on page 3 of the 752 manual. Use a standard high impedance meter for the signal voltages. I have had success with changing the 83 tube with a SS replacement as noted in the ARF posting. I do not want to wait 5-10 minutes to allow the 83 tube to warm up each time I check a tube, and there should be no issues with drift or changes over time. You should be able to get the proper line voltage and plate voltage with the SS replacement noted in the posting, you can always adjust the Zener diodes as needed to dial in the correct plate voltage. A few extra volts on the plate has an unmeasurable effect on GM. I also recommend using an external variac to set the line voltage and avoid the line sag issues with the internal rheostat. This has more to do with issues of maintaining the proper grid signal and heater voltage under testing, this was also recommended by Alltubetesters.

The military Hickok TV-10 manual is informative from a trouble shooting procedure and calibration instructions, although the 752 has far fewer adjustments. The manual is a bit large and can be downloaded from the following URL http://bama.edebris.com/download/mil...PS%2093021.pdf.
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Old 5th January 2012, 12:28 AM   #17
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Quote:
Originally Posted by glassandlight View Post
DO NOT USE DeOxit on any wafer or you just bought yourself a boat anchor. In fact, put deoxit in the next room with your stereo and away from test gear. It IS conductive oil and creates tiny leakage circuits a tester will pick up an a bad tube.
Not exactly accurate. Deoxit (previously Cramolin Red from Caig Industries) actually has a resistance of over 1 x 10e12 ohms/cm, which under contact pressure becomes negligable. BUT the solution MAY wash silver oxide partlcles between contacts creating a conductive path. When used correctly it should first be used as a cleaner, wiped away and then very lightly reapplied as a switch lubricant and anti-oxidizer. The problem arrises when people just squirt some of it out of either a can or hypo and then just leave it.
Doc
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Old 5th January 2012, 12:45 AM   #18
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mksj100:
Thanks for posting that URL to the AudioXpress Schoo artical. I thought I had saved it some time ago. And I did, but it was on a backup disc that I forgot about from an older computer.

dgta:
Sorry for throwing you a curve by saying my posted pdf was it.
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Old 5th January 2012, 12:49 AM   #19
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I agree with glassandlight about many of the Hickoks having the same voltages and similar circuit to achieve a proper test result for said tester. The voltages are identical on almost all of their tube based Mutual Conductance testers.
As is common with most aged components, they will drift in value thus the voltages will change also. The 5Y3 and 83 tubes are no exception to the aging process if used . I am of the opinion that one of the very first steps to check for proper calibration should be strong and balanced sections in both. Of course just because a tube is old does not mean that it is past it's prime. One of the main causes of a weak and unbalanced tube would be from excessive use or, hours of use. Calibrating to low value unbalanced tubes would only result in out of tolerance voltage readings and cause a false sense of accuracy under an actual load. And the Shunt/English pot, well, glassandlight said it all

Many end users of tube testers do not take the time to learn to read Hickoks schematics to see exactly what wire/switch/tubes do what. Hickok schematics are, at best, difficult to follow without the desire and time to understand them. Most of the users simply want to know that it is safe to use a tube in their audio equipment. For many of these folks, a calibration procedure for their exact tester would save them hours of time. Lots of free procedures out there on B.A.M.A.

I have read many conversations about the use of Deoxit or contact cleaners to clean the phenolic wafer switches. When you think about what you are cleaning from the switches is an oxidized form of the actual metal the contacts are made of, this makes for a better understanding. If you spray cleaners, especially oil based, all over the surface area of the switch, you impregnate the aged phenolic with the oxidized metal, or oil, causing small amounts of conductance to other contacts that could indeed give inaccurate readings, especially during leakage testing. Properly cleaning the contacts requires much time and patience to assure the phenolic does not get wet with the contaminents and must be removed with care.

Lots of good advice in this forum
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Old 5th January 2012, 11:55 AM   #20
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Quote:
Originally Posted by dgta View Post
Easy enough to test. Take a clean piece of plastic, make sure it tests as infinite resistance. Spray Deoxit. Let dry. Measure resistance again.
This is the last reply for me on this. YOU are kidding yourself. I suggest that you actually spray or slather it on the switch wafers and then test for a shorts and leakage and see what happens. The real test is here is to verify what I state as being true or false.

Back on the other thoughts kicked around here on the 83 and 5Y3, even tubes that test perfect for both em and gm can and will show peaks off by as much as 10% which does affect the gm reading. A scope is the only real way to find a tube with equal (or near equal) peaks..if you are aiming for as accurate a calibration as possible. Remember too, the plate and bias/screen supplies must be right before you can move on to testing shorts/leakage.

good luck everyone...over and out.
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